190
;
THE BIOLOGY OF FISHES
The principal cause of the variations in size seems…to
:
:
be a difference in the amount of yollç actually stored up f
in each ovum according to its position relative to the blood-'
Ï-“Ï
,
vessels in the ovary. The variation is thus to a great extent ;
'
,
due to chance and obeys the laws of chance occurrences, as .
can be seen from the following example (frein Heincke and
_
[l
Ehrenbau1n) of the size of Plaice eggs, from the same sh.
,
;
The “ lines
” refer to those on themicrometer of themicro-‘
'
60
61
62
63
.
64
_
‘
Observed values
.
.
2
52
112
29
4
200
Theoretical values
.
6
53
98
39
4
200 …
î
agreement is not so perfect as in the case of the
numberof Vertebræ in the Eel, yet sufcient to indiCate that
'
the diameter Of the eggs, thus their size, varies according to
the
of
occurrences.
The causal connection
between this variation” and that of any character, number
of vertebrae for example, has not yet been
out in f "‘-_j
detail, but as indicated above we can readily see that there is '
a connection.
With a difference in the size of the
balance of the sh is different When the vertebræ are
:":{gÎ
._
unless some other factor has come into play in the meantime;
"
Some"authors are not content With this simple relation, '_
however, and think that the sources of variation lie still»
,
more deeply, not—in theyolk, nor even in the general mass ÂOf
_
.
particular parts or chromosomesof
=
; thelatt
these the bearers not only
;,
ofthemhentancebutalso of the variation. .; For them the
PartlcularCharæt€fs of the îdiV‘idual are not supercial, '
personal,oracquired, that81deofthe matter is
.
Ï,
f
'
individual have
*jè
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come from” thos_e=o£,two?other,‘indiÿidualsg’gthesé- again from?
'
'—
four
fon Butth1s is pure asSump—’ LÏjf;
tmn 1f_the;
:
;
-_;
h but ltvvghtnthnhtd
-Byç: ,
ï
andehmlaüonWe may
tune ' the
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;